This invention relates to current sensors and, more particularly, to an alternating current sensor employing parallel-plate geometry and having a shunt for self-powering.
Current sensors, such as U.S. Pat. No. 5,066,904, entitled "Coaxial Current Sensors," by Bullock, issued Nov. 19, 1991, assigned to the assignee of the present invention and herein incorporated by reference, are known in the art. These sensors, although useful, suffer from some disadvantages including the need for an accurate current shunt which is meticulously designed for providing a highly accurate current measurement. For instance, use of such accurate shunt helps somewhat to reduce the size, weight, and expense of the current sensor by reducing the number of ampere-turns in the active part of the current sensor. However, even the use of an accurate current shunt typically introduces some expense due to the current sensor materials, such as low temperature coefficient materials, the large number of coil "turns" in the sensing and feedback coils of the current shunt, as well as the manufacturing care required to fabricate the current sensor. Thus, a need exists for a current sensor that overcomes these problems, that is, a current sensor that conveniently avoids the need of an accurate current shunt in order to provide an accurate current measurement.
Moreover, since current sensors typically have associated circuitry, such as signal conditioning circuits, signal processing circuits, control circuits and the like, it is also desirable for the current sensor to have a self-powering capability which allows for electrically powering such associated circuits in a manner which is essentially independent or separate from any current measurement or current sensing operation being performed in the current sensor. This is particularly desirable since the respective design and accuracy requirements of any current shunt and associated transformer that are employed both for current sensing and for self-powering, are typically much more demanding or restrictive than would be the respective design and accuracy requirements of a current shunt and associated transformer which are exclusively dedicated for self-powering. For example, this would advantageously allow for further reducing the size, weight, and cost of the current sensor due to the greater flexibility of design and lower expense of a current shunt and transformer which are exclusively dedicated for self-powering, as compared to a current shunt and transformer which must also provide highly accurate current measurements. Moreover, high-power circuit breaker applications generally require current sensors having a high dynamic range and accuracy while maintaining a relatively low cost and size.